The present invention relates to the art of semiconductor devices. It finds particular application in capacitive elements of extremely high integration density semiconductor chips and will be described with particular reference thereto. It is to be appreciated, however, the invention may also find application in conjunction with other semiconductor devices which incorporate dielectric insulators.
Heretofore, semiconductor memory devices have incorporated an integral storage capacitance construction. The capacitance construction normally included a pair of polycrystalline electrodes separated by a dielectric layer. Most commonly, the dielectric layer was a layer of silicon dioxide. In fabrication, the lower polycrystalline electrode was oxidized at an elevated temperature, e.g. 900.degree. C., to form the silicon dioxide insulating layer. The upper polycrystalline silicon electrode was deposited on the oxidized surface of the lower polycrystalline electrode. Although thermal oxidation is an effective technique for monocrystalline silicon, the high temperature oxidation of polycrystalline silicon creates problems. Thermally oxidized polycrystalline silicon commonly has a greater leakage current, a lower breakdown voltage, and more initial defects than thermally oxidized monocrystalline silicon.
Besides silicon dioxide, it has been suggested that other high permittivity dielectrid films, such as silicon nitride, tantalum oxide, or multiple layers of these films, could be utilized. See for example U.S. Pat. No. 4,151,607 to Koyanagi et al. issued Apr. 24, 1979 and U.S. Pat. No. 4,505,026 to Bohr et al. issued Mar. 19, 1985.
Japanese Patent Application No. 61-85857 to Kita, laid open May 1, 1986 discloses a multi-layered insulation construction. A 100 nm layer of polycrystalline silicon is low pressure chemically vapor deposited. A 20 nm layer of silicon nitride is low pressure chemically vapor deposited on the polycrystalline silicon layer. After etching, the silicon nitride layer is thermally oxidized to form a 2 nm layer of silicon dioxide. A polycrystalline silicon electrode layer was deposited on the silicon dioxide.
Neither these nor other multilayered insulation films proposed for capacitor insulation have proven satisfactory for capacitor insulation film. The proposed multilayered insulation films failed to achieve optimal capacitance characteristics, low leakage current, low defect occurrence, high reliability, high capacitance, and the like. Thick silicon nitride layers, such as a 20 nm layer, are more apt to fail and have a lower capacitance than thinner layers, particularly layers under 12 nm.
In accordance with the present invention, there is provided a new and improved dielectric insulation film which overcomes the above-referenced problems and others.